Neural correlates of visual consciousness

[Jeebus]

Are there some particular types of neurons, distributed over the visual neocortex, whose firing directly symbolizes the content of visual awareness? One very simplistic hypothesis is that the activities in the upper layers of the cortex are largely unconscious ones, whereas the activities in the lower layers (layers 5 and 6) mostly correlate with consciousness. I have wondered whether the pyramidal neurons in layer 5 of the neocortex, especially the larger ones, might play this latter role.

These are the only cortical neurons that project right out of the cortical system (that is, not to the neocortex, the thalamus or the claustrum). If visual awareness represents the results of neural computations in the cortex, one might expect that what the cortex sends elsewhere would symbolize those results. Moreover, the neurons in layer 5 show a rather unusual propensity to fire in bursts. The idea that layer 5 neurons may directly symbolize visual awareness is attractive, but it still is too early to tell whether there is anything in it.

Visual awareness is clearly a difficult problem. More work is needed on the psychological and neural basis of both attention and very short-term memory. Studying the neurons when a percept changes, even though the visual input is constant, should be a powerful experimental paradigm. We need to construct neurobiological theories of visual awareness and test them using a combination of molecular, neurobiological and clinical imaging studies -- Francis Crick and Christof Koch.

I believe that once we have mastered the secret of this simple form of awareness, we may be close to understanding a central mystery of human life: how the physical events occurring in our brains while we think and act in the world relate to our subjective sensations—that is, how the brain relates to the mind.

Postscript from Francis Crick and Christopher Koch: There have been several relevant developments since this article was first published. It now seems likely that there are rapid "on-line" systems for stereotyped motor responses such as hand or eye movement. These systems are unconscious and lack memory. Conscious seeing, on the other hand, seems to be slower and more subject to visual illusions. The brain needs to form a conscious representation of the visual scene that it then can use for many different actions or thoughts. Exactly how all these pathways work and how they interact is far from clear.

There have been more experiments on the behavior of neurons that respond to bistable visual percepts, such as binocular rivalry, but it is probably too early to draw firm conclusions from them about the exact neural correlates of visual consciousness. We have suggested on theoretical grounds based on the neuroanatomy of the macaque monkey that primates are not directly aware of what is happening in the primary visual cortex, even though most of the visual information flows through it. This hypothesis is supported by some experimental evidence, but it is still controversial.

What do you PF hypothes-izers think of this?

 

[Mentat]

Originally posted by Jeebus
What do you PF hypothes-izers think of this?

I think you are right about the possible ramifications of this kind of discovery.

Personally, I really like William H. Calvin's hypothesis on this (as put forth in The Cerebral Code: Thinking a thought in the Mosaics of the mind), which is a selectionist idea (basically, the idea that Darwinian processes (not just natural selection, but all of the Darwinian evolutionary processes) in the neocortex are what produce conscious experience), but with an extra facet: He thinks he's identified the most fundamental structure of perception, the "stupid demons" of Dennett's theory, the so-called "Hebbian" (after Donald Hebb) cell-asemblies. He believes that they are hexagonal patterns of synchronously firing pyrimidal interneurons, each from its own triangular array. IOW, the synchronously-firing neurons form triangular arrays of "flashing" self-stimulation (that's leaving aside the spatiotemporal "new" firings, in which case self-stimulation would obviously not be necessary), and one member from each array fires along with five other neurons (each a member of another array) thus producing hexagonal shape, with a "hot-spot" in the center.

This is an over-view, and I probably couldn't explain it as well as he can, so you should probably read the book. Be warned, however: if anything that I said above seemed "beyond" what you're used to (more technical than you can "keep up with") use the glossary constantly (and keep a dictionary handy too...or, at least, I do ) .

 

[Mentat]

Has anyone heard of Calvin's hexagon theory before?

 

[Yahweh]

Originally posted by Jeebus
What do you PF hypothes-izers think of this?

Its already been established that Internal Monologue (which arises from the Corpus Callosum) plays a major part in self-awareness.

There are no "consciousness neurons", but all the parts of your brain work together to make humans the conscious devils that they are. (Devils? )

 

[Mentat]

Originally posted by Yahweh
Its already been established that Internal Monologue (which arises from the Corpus Callosum) plays a major part in self-awareness.

There are no "consciousness neurons", but all the parts of your brain work together to make humans the conscious devils that they are. (Devils? )

I agree with most of this...but, please be more specific as to how the Corpus Callosum produces Internal Monologue.